Nitrification In Distribution Systems Research Articles

Abundance and activity of ammonia oxidizing archaea and bacteria in bulk water and biofilm in water supply systems practicing chlorination and chloramination: Full and laboratory scale investigations.

The abundance and nitrification activity of ammonia oxidizing archaea (AOA) and ammonia oxidizing bacteria (AOB) in bulk water and biofilm in chloraminated and chlorinated water supply systems were investigated. The abundance of AOB varied between cold and warm periods while that was the case for AOA only in biofilm. Lower ammonia concentrations favored the abundance of AOA over AOB. AOA and AOB were found more in distal zones of the distribution system (DS). Higher numbers of AOA and AOB were observed in DS associated with chloramination compared to those associated with chlorination. Significant positive correlations between ammonia-N in bulk water and AOA indicate a possibility of involvement of AOA in nitrification in DS. A separate laboratory-based experiment simulating DS condition was conducted to understand the effects of chlorine and chloramine dosages and temperature on AOA and AOB. AOA were inhibited less than AOB in the presence of lower concentrations of chlorine and chloramine (1.5 and 2.0mg/L chlorine; 0.05-0.1 and 0.3-0.4mg/L chloramine) while both of them were not detected at higher dosages (2.5mg/L chlorine and 1.5-1.6mg/L chloramine). At a low temperature (10-12°C), chloramine and chlorine provided similar inhibition trends in which AOB were inhibited more than AOA. At a high temperature (25°C), chloramine was less inhibitory to AOA and AOB than chlorine.

Impact of NOM character on copper adsorption by trace ferric hydroxide from iron corrosion in water supply system

The fate of trace concentrations of cupric sulfate (<0.4mg/L) dosed into chloraminated distribution systems to inhibit nitrification has been shown in this study to be controlled by at least two crucial factors: the character of natural organic matter (NOM) and iron hydroxide corrosion products present at low concentrations (<2mg/L). This research quantified the removal of Cu(II) ions added into waters containing trace Fe(OH)3 flocs and the effect of NOM of different character on this removal. The dominant dissolved copper species in NOM-containing waters were found to be Cu(II)–NOM complexes. Both intramolecular chelation and intermolecular complexation can occur, with the latter occurring preferentially and resulting in the aggregation of smaller organic molecules to form larger molecules. The presence of ferric hydroxide flocs when Cu(II) ions were added into NOM-containing waters was shown to result in removal of Cu(II) ions, presumably as Cu(II)–NOM complexes. This removal was through adsorption processes obeying Freundlich isotherms, although the presence of larger NOM molecules and heterogeneous copper species (e.g. Cu(OH)2(s) and CuO(s)) appeared to shield smaller Cu(II)–NOM complexes from adsorption to some extent. For the strategy of inhibition of nitrification in distribution systems by the addition of Cu(II) ions, complexation of Cu(II) ions by NOM and adsorption of Cu(II)–NOM complexes by ferric hydroxide flocs released from pipe walls pose significant operational challenges to maintaining the concentration of Cu(II) ions through the distribution system.

Onset of severe nitrification in mildly nitrifying chloraminated bulk waters and its relation to biostability

Triggers of severe nitrification in distribution systems are still not clearly understood. Recently, the biostability concept was proposed to explain the chloramine residual below which signs of nitrification would be seen. To improve understanding, mildly nitrifying bulk water samples (nitrite less than 0.010 mg-N/L) from Sydney Water distribution systems were incubated at constant temperatures and periodically analysed for nitrogenous compounds and total chlorine. Total ammoniacal nitrogen in the sample was between 0.25 and 0.35 mg-N/L. Severe nitrification was triggered when chloramine residuals dropped below about 0.4 mg/L – the critical threshold residual. In 45 such samples, the critical threshold residual was 0.2–0.65 mg/L. The biostability concept was found to be useful in explaining the residual below which net growth of microorganisms begins. However, this alone could not predict the critical threshold residual. Different means of overcoming this problem are discussed. One of these is the use of the microbial decay factor method, since microbiologically assisted chloramine decay in the samples studied was found to be mostly the result of ammonia-oxidising bacterial activity. Nitrite levels in winter were found to be poor indicators of nitrifying status. Overall the results were found to be useful in controlling nitrification and to obtain early warning of severe nitrification.

Potential side effects of using ammonia to inhibit bromate formation during the ozonation of drinking water

This note identifies potential side effects of using ammonia to inhibit bromate formation during the ozonation of drinking water, and makes preliminary predictions of their significance. Based on kinetic calculations, it is expected that ammonia would not exert a significant ozone demand and consequently would have little impact on the ozonation process. The ammonia needed to inhibit bromate formation is also not expected to promote nitrification in distribution systems, since the ammonia would either typically be removed through breakpoint chlorination or would be used to form chloramines. However, the impact of ammonia on biologically active filters, which often follow ozonation, is more difficult to evaluate since the issue has not been directly studied, and the role of nitrogen in the biological processes in such an environment is complex. Further, if chlorine were being used for secondary disinfection, any ammonia that persisted in the treated water would exert a demand and would have to be considered.

Disinfectant efficacy of chlorite and chlorine dioxide in drinking water biofilms

The drinking water industry is closely examining options to maintain disinfection in distribution systems. In particular this research compared the relative efficiency of the chlorite ion (ClO 2 −) to chlorine dioxide (ClO 2) for biofilm control. Chlorite levels were selected for monitoring since they are typically observed in the distribution system as a by-product whenever chlorine dioxide is applied for primary or secondary disinfection. Previous research has reported the chlorite ion to be effective in mitigating nitrification in distribution systems. Annular reactors (ARs) containing polycarbonate and cast iron coupons were used to simulate water quality conditions in a distribution system. Following a 4 week acclimation period, individual ARs operated in parallel were dosed with high (0.25 mg/l) and low (0.1 mg/l) chlorite concentrations and with high (0.5 mg/l) and low (0.25 mg/l) chlorine dioxide concentrations, as measured in the effluent of the AR. Another set of ARs that contained cast iron and polycarbonate coupons served as controls and did not receive any disinfection. The data presented herein show that the presence of chlorite at low concentration levels was not effective at reducing heterotrophic bacteria. Log reductions of attached heterotrophic bacteria for low and high chlorite ranged between 0.20 and 0.34. Chlorine dioxide had greater log reductions for attached heterotrophic bacteria ranging from 0.52 to 1.36 at the higher dose. The greatest log reduction in suspended heterotrophic bacteria was for high dose of ClO 2 on either cast iron or polycarbonate coupons (1.77 and 1.55). These data indicate that it would be necessary to maintain a chlorine dioxide residual concentration in distribution systems for control of microbiological regrowth.

Occurrence of nitrifying bacteria and nitrification in Finnish drinking water distribution systems

Microbiological nitrification process may lead to chemical, microbiological and technical problems in drinking water distribution systems. Nitrification activity is regulated by several physical, and chemical, and operational factors. However, the factors affecting nitrification in the distribution systems in boreal region, having its specific environmental characteristics, are poorly known. We studied the occurrence and activity of nitrifying bacteria in 15 drinking water networks distributing water with very different origin and treatment practices. The waters included chloraminated surface water, chlorinated surface water, and non-disinfected groundwater. The networks were located in eight towns in different parts of Finland. Our results showed that nitrifying bacteria are common in boreal drinking water distribution systems despite their low temperature. Surprisingly high numbers and activities of nitrifiers were detected in pipeline sediment samples. The numbers of ammonia-oxidizing bacteria and their oxidation potentials were highest in chloraminated drinking water delivering networks, whereas the nitrite-oxidizing bacteria were present in the greatest numbers in those networks that used non-disinfected groundwater. The occurrence of nitrifying bacteria in drinking water samples correlated positively with the numbers of heterotrophic bacteria and turbidity, and negatively with the content of total chlorine. Although nitrifying bacteria grew well in drinking water distribution systems, the problems with nitrite accumulation are rare in Finland.

Using chlorite ion to control nitrification

Laboratory and field studies of five Texas distribution systems suggest that chlorite ion has significant potential for controlling nitrification in chloraminated water.Controlling nitrification is essential if chloramines are to be a viable alternative disinfectant scheme for distribution systems in all types of environments. This article reviews problems associated with nitrification and presents laboratory and field evidence for using the chlorite ion (ClO2–) to control nitrification in distribution systems. Laboratory experiments in this study showed that even low dosages of ClO2– (0.05 mg/L) can inactivate 3–4 logs of ammonia‐oxidizing bacteria (AOB) over several hours. Higher concentrations of ClO2– inactivate all of the AOB in as little as 30 minutes. Field investigations at five Texas water utilities showed that the presence of ClO2– in the distribution systems resulted in less loss of chloramines and ammonia–nitrogen and thus less nitrification than in those systems in which ClO2– was not present. The ease of use of ClO2– is compared with other, more traditional nitrification control measures.

Advances in Treatment Processes to Solve Off-Flavor Problems in Drinking Water

There have been significant advances in the development and application of treatment processes to control off-flavor problems in drinking water in the past few years. This paper updates two major treatment process summaries that appeared in 1988 and 1995. The paper also puts the efficiencies of the treatment processes in perspective by using the drinking water flavor wheel as a reference point. Removal or control of classes of off-flavor problems are described in relation to the categories on the wheel. Specifically, processes such as oxidation, adsorption, biological treatment and membranes are described. The recent literature is reviewed and advances in treatment are identified. A new treatment process for controlling nitrification in distribution systems is introduced which has the potential to dramatically reduce the problems of chlorinous odor complaints from customers.

Advances in treatment processes to solve off-flavor problems in drinking water

There have been significant advances in the development and application of treatment processes to control off-flavor problems in drinking water in the past few years. This paper updates two major treatment process summaries that appeared in 1988 and 1995. The paper also puts the efficiencies of the treatment processes in perspective by using the drinking water flavor wheel as a reference point. Removal or control of classes of off-flavor problems are described in relation to the categories on the wheel. Specifically, processes such as oxidation, adsorption, biological treatment and membranes are described. The recent literature is reviewed and advances in treatment are identified. A new treatment process for controlling nitrification in distribution systems is introduced which has the potential to dramatically reduce the problems of chlorinous odor complaints from customers.

Occurrence of nitrification in chloraminated distribution systems

Data from US distribution systems that chloraminate are evaluated as predictors of nitrification.Utilities in the United States that chloraminate were surveyed to evaluate the incidence of nitrification in distribution systems and determine whether nitrification can be predicted from basic system and water quality data. An estimated two thirds of medium and large US systems that chloraminate experience nitrification to some degree. About every fourth surveyed utility reported moderate to severe nitrification problems. In addition, every fourth utility did not know the extent of nitrification in its system. The incidence of nitrification was more frequent during summer or when the temperature was greater than 15°C (59°F); nevertheless, several sites sampled under cold water conditions—i.e., below 10°C (50°F)—also evidenced nitrification. No one water quality parameter by itself may be a good indicator of nitrification, but several important factors should be evaluated collectively—nitrite, nitrate, chloramine dosage and residual, ammonia, pH, heterotrophic bacterial counts, and dissolved oxygen.